Magnetoresistive components, such as permalloy, can be utilized in a variety of sensing applications, such as, for example, in the contactless detection of changes in state, such as the measurement of an angular position of a rotatably mounted part. Magnetoresistive-based sensors typically include magnetic field-dependent resistors, which are arranged in a bridge circuit configuration and through which a control current is fed. When a magnetoresistive-based sensor is influenced by a magnetic field, a voltage can be established in which the magnitude of the voltage depends on the magnitude and direction of the magnetic field associated with the sensor.
The relationship between an associated bridge circuit voltage and the magnetic field direction can be utilized in a contactless magnetoresistive sensor, for example, to detect the angular position of a rotatably mounted part. Such sensors are particularly useful in automotive applications. Magnetoresistive sensors are typically configured from a magnetoresistive film that is formed from a magnetic substance that exhibits a magnetoresistive effect and generally possesses a single active layered structure.
A magnetoresistive sensor may be acted upon by a magnetic field oriented in a particular manner, such that a definite control current can be applied to the current contacts of an associated bridge circuit. The voltage that is then established at the other contacts can be measured on an ongoing basis. In general, the pattern of magnetoresistive material utilized in magnetoresistive sensors can be connected electrically in a Wheatstone bridge arrangement in order to sense changes in the resistance of the magnetoresistive material in response to changes in the strength and direction of a magnetic field component in the plane of the magnetoresistive elements. In order to monitor the changes in the resistance of the material, associated components, such as amplifiers, are generally connected together to form an electrical circuit, which provides an output signal that is representative of the strength and direction of the magnetic field in the plane of the sensing elements.
When the circuit is provided on a silicon substrate, for example, electrical connections between associated components can be made above the surface of the silicon or by appropriately doped regions beneath the components and within the body of the silicon substrate. Components can be connected to each other above the surface of the silicon by disposing conductive material to form electrically conductive paths between the components. When appropriately doped regions within the silicon substrate connect components in electrical communication with each other, an electrically conductive path can be formed by diffusing a region of the silicon with an appropriate impurity, such as phosphorous, arsenic or boron to form electrically conductive connections between the components.
Permalloy is often utilized in Magnetoresistive-based sensing applications that require increasing sensitivity. Note that as utilized herein, the term “permalloy” generally refers to any of several alloys of nickel and iron having high magnetic permeability. Typical permalloy-based magnetoresistive devices utilize the small electrical resistance change of the permalloy film to a magnetic field by forcing a current through the resistor and measuring the voltage change. This is often accomplished in a Wheatstone bridge configuration with many resistors arranged electrically in series per bridge element to maintain the current low and the sensitivity high.
Recent activity has indicated that the direction of anisotropy greatly affects the low field sensitivity of permalloy. One of the primary problems with conventional techniques of producing permalloy is that the anisotropy thereof is defined at deposition, or a later time. The anisotropy can only be set, however, for the entire substrate or wafer utilized in the production process.
Anisotropy, an important factor in permalloy-based detection devices, can be defined as the tendency of a material to react differently to stresses applied in different directions or the characteristics of exhibiting different values of a property in different directions with respect to a fixed reference system in the material. Based on the foregoing, it is believed that a need exists for a new technique that provides for improved sensitivity of permalloy based sensing devices, especially for low field (i.e., near zero Gauss) applications. It is believed that the unique methods and systems disclosed herein solve these needs.